Crossed-field microwave tube having a fluid cooled cathode and control electrode

ABSTRACT

A crossed-field microwave tube includes a generally cylindrical central electrode structure having an arcuate cathode emitter portion and a sector-shaped control electrode portion. The cathode emitter is carried in heat exchanging relation upon the outside of a double walled cathode support tube. The annular space between the double walls defines a cathode fluid coolant passageway. The control electrode is carried from a tubular support member centrally disposed of the cathode support tube. Fluid coolant passes in series through the control electrode support tube and the outer annular cathode coolant passageway. The control electrode support tube includes a tubular insulator defining a portion of control electrode coolant passageway.

United States Patent Andrew S. Wilczek Old Bridge;

Charles Gill, Newark, both of NJ. 832,901

June 13, 1969 Oct. 12, 1971 Varian Associates Palo Alto, Calif.

Inventors Appl. No. Filed Patented Assignee Int. Cl 110131 02, 1101 23/04 Field of Search 313 19, 23,

Primary Examiner-Roy Lake Assistant Examiner-E. R. LaRoche Attorneys-Stanley Z. Cole and Gerald L. Moore ABSTRACT: A crossed-field microwave tube includes a generally cylindrical central electrode structure having an arcuate cathode emitter portion and a sector-shaped control electrode portion. The cathode emitter is carried in heat exchanging relation upon the outside of a double walled cathode support tube. The annular space between the double walls defines a cathode fluid coolant passageway. The control electrode is carried from a tubular support member centrally disposed of the cathode support tube. Fluid coolant passes in series through the control electrode support tube and the outer annular cathode coolant passageway. The control electrode support tube includes a tubular insulator defining a portion of control electrode coolant passageway.

CROSSED-FIEILD MICROWAVE TUBE HAVING A FLUID COOLED CATE'IODE AND CONTROL ELECTRODE DESCRIPTION OF THE PRIOR ART Heretofore, crossed-field microwave tubes have employed coolant passageways for cooling the cathode emitter and the control electrode structure. However, in these prior tubes, the control electrode structure was mounted to its fluid cooled support structure via the inten'nediary of a sector shaped insulative member, as of beryllia. Heat was removed from the control electrode structure by thermal conduction through the beryllia insulative member to the fluid cooled support structure. The problem with this arrangement is that the beryllia insulative structure had to be segmented in a wafflelike pattern in order to allow for the unequal rates of thermal expansion between the insulative member and the control electrode member. As a consequence, the thermal conductivity of the segmented insulative structure was relatively low, resulting in relatively poor cooling of the control electrode, thereby restricting the operating power level of the tube.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved crossed-field microwave tube having a fluid cooled cathode and control electrode.

One feature of the present invention is the provision of a tubular control electrode support structure with the control electrode being electrically connected to the tubular support member in heat exchanging relation therewith and including means for directing a fluid coolant through the tubular support structure for cooling the control electrode in use.

Another feature of the present invention is the provision of a tubular insulator interconnecting the tubular control electrode support member and the remaining portion of the coolant passageway such that the tubular insulator forms a portion of the fluid passageway of the control electrode structure.

Another feature of the present invention is the same as any one or more of the preceding features wherein the cathode emitter is affixed to a cylindrical support structure having a double wall construction to define an annular cathode coolant passageway with the annular cathode coolant passageway being connected in series fluid communication with the control electrode fluid passageway.

Another feature of the present invention is the same as the preceding feature including the provision of a plurality of thermally conductive fins axially coextensive with the cathode portion and being disposed in the annular cathode fluid coolant passageway for enhancing the transfer of heat from the cathode to the fluid coolant.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a transverse schematic line diagram of a prior art crossed-field microwave tube incorporating a control electrode structure, and

FIG. 2 is an enlarged longitudinal sectional view of a composite cathode and control electrode structure incorporating features of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown a typical prior art crossed-field amplifier tube 1. Briefly, the tube 1 includes a central cathode electrode structure 2 surrounded by an anode electrode 3. The anode electrode 3 includes a microwave circuit portion 4 such as an array of strapped bars. A circuit sever 5 defines an input terminal 6 of the circuit 4, adjacent one side of the circuit sever 5, and an output terminal 7 adjacent the other end of the sever 5.

The central electrode structure 2 is generally cylindrical in shape and includes a cathode emitter portion 8 and a sectorshaped control electrode portion 9 insulatively supported relative to the cathode emitter portion 8 to permit an independent potential to be applied to the control electrode relative to that of the cathode portion 8. An annular reentrant stream crossed-field interaction region I1 is defined by the annular space between the central electrode structure 2 and the surrounding anode electrode 3. A magnet structure, not shown, produces an axially directed magnetic field H in the interaction region 11.

In operation, microwave energy to be amplified is applied to the input terminal of the circuit 4 via an input coaxial line 12. The microwave energy on the circuit 4 interacts with an electron stream U in the crossed-field interaction region 11 to produce an amplified microwave signal on the circuit 4 which is extracted from the output end 7 of the circuit 4 via an output coaxial line 14 and transmitted to a suitable load, such as an antenna, not shown. The input microwave energy comprises a series of pulses and is of sufficient amplitude to produce back electron bombardment of the cathode 8 to provide a copious emission of secondary electrons from the cathode 8 to contribute to the electron stream 13. The tube 1 is turned off by applying a positive potential to the control electrode 9 relative to the potential of the cathode portion 8, such that the electron stream is collected on the control electrode 9. The control electrode 9 is pulsed positive, simultaneously with the termination of each of the input microwave pulses, to terminate amplification of the input energy.

If it were not for operation of the control electrode 9, the reentrant nature of the electron stream would permit the tube to amplify noise energy coupled from the stream onto the circuit 4. The noise energy on the circuit would produce RF electric fields in the electron stream to drive certain electrons back into the cathode secondary emitter to produce secondary emission to sustain the electron stream and the tube would break into sustained oscillation at a frequency within the passband of the circuit 4. Thus, the control electrode 9 is employed for terminating operation of the tube upon termination of each of the input pulses of RF energy to be amplified. During operation of the tube, substantial electron back-bombardment of the cathode 8 produces heating thereof and it is desired that this thermal energy be removed from the cathode such that it does not become a thermionic emitter. Also, it is desired that the control electrode 9 be cooled since it collects substantial power during the turnoff period.

Referring now to FIG. 2, there is shown a central electrode structure 2 incorporating features of the present invention. The central electrode structure 2 includes a hollow cylindrical cathode support structure 17 formed of a double wall construction having an outer tubular wall 18 and a closely spaced coaxial inner wall 19. The walls are made of a refractory metal such as molybdenum and are of relatively thin wall construction, as of 0.025 inch thick. The arcuate cathode emitter 8, as of barium impregnated tungsten, is brazed to an arcuate support member 21, as of molybdenum, which in turn is brazed to the outer surface of the cylindrical cathode support I7. A pair of radially directed flange members 22 and 23, as of molybdenum, are brazed to the outer wall 18 of the cathode support 17 at opposite axial ends of the cathode emitter 8. The flanges 22 and 23 form end hat structures for the cathode emitter 8.

The double wall construction of the cathode support structure 17 defines an annular cathode fluid coolant passageway 24 in the space therebetween. In a typical example, the radial spacing between the tubular members 18 and 19 is approximately 0.1 inch and the outside diameter of the cathode support 17 is approximately 1 inch. A plurality of closely spaced metallic fins 25, as of molybdenum, are brazed in position between the inner and outer walls 19 and 18, respectively, of the cathode support 17. The fins 25 are axially coextensive with the cathode 8 to enhance transfer of thermal energy from the cathode 8 through the support 21, wall 18, and fins 25 to the fluid coolant, such as water, which passes in the axial direction through the annular cathode coolant passageway 24.

A sector shaped portion of the cathode support structure 17 is cut away at 20 for approximately 60 of arc to accommodate the sector shaped control electrode 9, as of molybdenum. The axial ends of the cutaway portion 20 of the cathode support structure K7 are closed by means of a pair of arcuate end wall structures 26 brazed between the inner and outer walls 19 and i8, respectively, of the cathode support 17. The side portions of the cutaway section 20 of the cathode support 17 are closed by means of a pair of the fins 25 which are sealed at their axial ends to the arcuate closing members 26.

The control electrode 9 is supported from a tubular metallic support member 27, as of copper, coaxially disposed of the cathode support structure 17, via the intermediary of a thermally and electrically conductive block 2%, as of copper. The copper block 28 is apertured to receive the tubular support member 27 and is brazed to the support member 27 and to the control electrode 9 to facilitate thermal conduction from the control electrode 9 to the central support tube 27. The interior of the tubular control electrode support 27 forms a fluid coolant passageway for removing heat conducted to the tube 27 from the control electrode 9. The upper end of the control electrode support tube 27 is interrupted by means of a hollow cylindrical insulator 29, as of alumina ceramic, which is brazed at is ends to the tube 27. in this manner, the insulator 29 forms a portion of the tubular control electrode support structure and also defines a portion of the fluid control electrode coolant passageway through the tubular support structure 27.

The upper end of the cathode support structure 17 is closed off by means of a metallic disk 31 sealed at its periphery, as by brazing, to the outer tubular wall 18. An annular metallic disk 32 is sealed at its outer and inner periphery, as by brazing, to the upper end of the inner wall 19 and to the upper end of the tubular control electrode support 27, respectively. Thus a coolant distribution manifold 33 is defined in the axial end space between annular disk 32 and disk 31.

The distribution manifold 33 serves to connect the outer annular cathode coolant passageway 24 in series fluid communication with the central control electrode fluid passageway, within tube 27, such that fluid coolant flowing in the upward direction through annular cathode coolant passageway 24 is collected at the manifold 33 and redirected in the axial direction down through the central tubular passageway 27. A suitable fluid coolant is deionized distilled water having a resistivity of approximately 1 megohm cm.

When the tube 1 is amplifying input microwave energy, the control electrode 9 and the cathode 8 are operated at the same potential, as of -30 kv. relative to the anode potential. When the control electrode 9 is to collect the electron stream and to terminate amplification, the control electrode 9 is pulsed to a potential more positive than the cathode potential, as to l kv. The tubular insulator 29, as of 0.750 inch long, is found sufficient to hold off the kv. potential applied between the control electrode 9 and the cathode 8 even in the presence of the fluid coolant flowing through the two electrode support structures. Typical fluid coolant flow rates are 2.5 gallons per minute. With this flow rate, approximately 2.5

kw. of average back heating power is dissipated by the coolant flowing through the cathode cooling fins 25 such that the temperature of cathode emitter 3 remains below at approximately 300 C.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a crossed-field microwave tube, means forming a central electrode structure having a first portion defining a cathode electrode and a second portion defining a control electrode, means forming an anode electrode structure surrounding said central electrode structure and having a microwave circuit formed therein facing said central electrode structure to define an annular crossed-field interaction region in the space between said anode and cathode, said control electrode comprising a sector of said central electrode structure, means for insulatively supporting said control electrode sector relative to said cathode portion of said central electrode structure, the improvement wherein, said support means for said control electrode includes a tubular support member disposed within said central electrode structure, said control electrode being electrically connected to said tubular support member in heat exchanging relation therewith, and means for directing a fluid coolant through said tubular support member for cooling said control electrode in use.

2. The apparatus of claim 1 wherein said central electrode structure includes an outer cylindrical wall, and further including a second tubular metallic member coaxially disposed of and within said central electrode structure between said tubular control electrode support member and the outer cylindrical wall of said central electrode structure to define with the outer wall of said central electrode structure an annular cathode coolant fluid passageway disposed in heat exchanging relation with said cathode electrode for cooling same in use.

3. The apparatus of claim 2 including a plurality of metallic fins disposed in said annular cathode coolant fluid passageway, said fins being axially coextensive with said cathode portion of said central electrode structure to enhance transfer of heat from said cathode to the fluid coolant.

4. The apparatus of claim 2 including a coolant manifold structure disposed within said central electrode structure for connecting the control electrode fluid coolant passageway in said tubular control electrode support member in series fluid communication with said annular cathode coolant passageway to form a composite control electrode and cathode electrode fluid coolant passageway, and a tubular insulator member mechanically interconnecting a portion of said tubular control electrode support member and said coolant manifold structure for holding off the electrical potential applied in use between said cathode electrode and said control electrode.

5. The apparatus of claim 4 wherein the interior of said tubular insulator defines a portion of the composite series fluid coolant passageway. 

1. In a crossed-field microwave tube, means forming a central electrode structure having a first portion defining a cathode electrode and a second portion defining a control electrode, means forming an anode electrode structure surrounding said central electrode structure and having a microwave circuit formed therein facing said central electrode structure to define an annular crossed-field interaction region in the space between said anode and cathode, said control electrode comprising a sector of said central electrode structure, means for insulatively supporting said control electrode sector relative to said cathode portion of said central electrode structure, the improvement wherein, said support means for said control electrode includes a tubular support member disposed within said central electrode structure, said control electrode being electrically connected to said tubular support member in heat exchanging relation therewith, and means for directing a fluid coolant through said tubular support member for cooling said control electrode in use.
 2. The apparatus of claim 1 wherein said central electrode structure includes an outer cylindrical wall, and further including a second tubular metallic member coaxially disposed of and within said central electrode structure between said tubular control electrode support member and the outer cylindrical wall of said central electrode structure to define with the outer wall of said central electrode structure an annular cathode coolant fluid passageway disposed in heat exchanging relation with said cathode electrode for cooling same in use.
 3. The apparatus of claim 2 including a plurality of metallic fins disposed in said annular cathode coolant fluid passageway, said fins being axially coextensive with said cathode portion of said central electrode structure to enhance transfer of heat from said cathode to the fluid coolant.
 4. The apparatus of claim 2 including a coolant manifold structure disposed within said central electrode structure for connecting the control electrode fluid coolant passageway in said tubular control electrode support member in series fluid communication with said annular cathode coolant passageway to form a composite control electrode and cathode electrode fluid coolant passageway, and a tubular insulator member mechanically interconnecting a portion of said tubular control electrode support member and said coolant manifold structure for holding off the electrical potential applied in use between said cathode electrode and said control electrode.
 5. The apparatus of claim 4 wherein the interior of said tubular insulator defines a portion of the composite series fluid coolant passageway. 